Optical data storage media such as CD's (Compact Discs), DVD's (Digital Video Discs or Digital Variety Discs), DVD-ROM, and CDROM's are used to distribute software, games, movies, and the like. Limited lifetime versions have been developed, e.g. by Flex-play Technologies, Inc. and Spectra-Disc, that are playable for a limited amount of time, e.g. between 15 and 48 hours. Examples of this technology are disclosed in U.S. Pat. No. 5,815,484 (Smith et al.), U.S. Pat. No. 6,338,933 (Lawandy et al.), U.S. Pat. No. 6,343,063 (Rollhaus et al.), and U.S. Pat. No. 6,011,772 (Rollhaus et al.), all incorporated herein by reference in their entirety. These technologies would allow for example, point-of-purchase of movies that would not have to be returned, because after a limited time the disc will no longer play, i.e. become inactive.
One method to make limited lifetime discs is to incorporate a layer within them that contains a dye in a transparent reduced (leuco) form. Upon exposure to oxygen for a period of time, e.g. oxygen from air, the leuco dye oxidizes and becomes optically colored or darkened. This chemical reaction and resulting color change effectively blocks the interrogating laser beam used to read the data. This can be incorporated for example into various DVD formats including DVD-5, DVD-9, DVD-18 and the like. Other technologies achieve limited play life by incorporating chemistry that causes, in the presence of oxygen, the reflective metallic coating to oxidize or corrode. The oxidized or corroded metallic coating can not then accurately reflect the interrogating laser beam used to read the data.
A shelf life of between 6 and 12 months is highly desirable for such oxygen-sensitive optical discs. Unfortunately, even in a rigorously gas flushed and/or vacuum high barrier package sufficient oxygen is often present to oxidize the dye used to block the laser beam. The oxygen may be dissolved in the polycarbonate (PC) disc and/or trapped in the small headspace in the package. Because of the thickness and OTR (oxygen transmission rate) of typical optical discs, it requires about 24 hours to de-oxygenate the PC by inert gas flushing, which is an impractical packaging scenario. A failure to control and limit the presence of oxygen will result in premature disabling of the optical disc. While polycarbonate is currently the material of choice in the manufacture of optical discs, dissolved oxygen and oxygen diffusion issues would also be present in any other polymer that may be used to manufacture optical discs. Polymers that may be selected for optical disc manufacture include acrylic polymers and copolymers, polyamides, polymethylpentene, ethylene/norbornene copolymers, polyesters, and styrenic polymers.
In order to have reasonable shelf life through distribution, these limited lifetime discs can benefit greatly from oxygen scavenging packaging.
One form of oxygen scavenging packaging is oxygen scavenging sachets. These could be used in a MAP (modified atmosphere) package, but unfortunately can be costly, and aesthetically difficult to accommodate in a package containing a typically thin optical data storage medium such as a CD or DVD.
It has now been found that a primary vacuum or MAP (modified atmosphere) package in the form of a thermoformed package, that additionally incorporates an oxygen scavenger in either or both of a thermoformed (preferably bottom) web and a covering (preferably non-formed and preferably top) web, can prevent premature disabling or inactivation of an optical data storage medium before the intended lifetime of the medium is reached. Since the preferred package format is a vacuum package, an oxygen scavenger relatively uniformly dispersed in the film is preferred over sachets and the like. This is because, in a tight vacuum package, a sachet tends to provide oxygen scavenging activity that is physically localized and therefore functionally limited to its position in the package. In contrast, an oxygen scavenging film which physically forms at least a portion of the primary packaging material, e.g. as a continuous or semi-continuous layer or coating, will effectively scavenge oxygen in whatever portion of the package the scavenger is present.
The inventors have found that a package of the type described above can incorporate an oxygen scavenger in the form of a layer or coating, preferably along with at least one of several other useful features. These include means for opening the package, a means for identifying the package (authentication), an anti-theft feature, a means of tracking and/or inventory management, and printing (graphics).